The thermochemistry of M(CO)6−xLx (M = Cr,Mo, W; L = piperidine,pyridine, pyrazine,pyrazole, thiazole; x = 1, 2, 3)

A number of M(CO)_6?xL_x complexes (M = Cr, Mo, W; L = piperidine, pyridine, pyrazine, pyrazole, thiazole; x = 1, 2, 3) are shown to undergo both disproportionation and substitution in a CO atmosphere, when heated on a thermobalance. Using a DSC, reaction enthalpies have been determined from which enthalpies of formation were calculated. Combined with the sublimation enthalpies of these complexes, individual metal—ligand bond enthalpies were evaluated and discussed.     

Magnetic properties in the system (La1−xCax)CoO3 (0≦ x ≦ 0.6)

The perovskite (La_1?xCa_x)CoO₃ (0 ≦ x ≦ 0.6) was prepared under high oxygen pressures. The rhombohedral distortion decreases with increasing x and the phase becomes cubic at x = 0.5. From the results of magnetic measurement, it was found that the cobaltite with $\text{x ≧ 0.05}$ is ferromagnetic. This result is explained by the itinerant-electron model.     

Electrical properties in the system (La1−xCax)CoO3 (0.1 ≦ x ≦ 0.5)

The electrical resistivity of (La_1?xCa_x)CoO₃ (0.1 ≦ x ≦ 0.5) was measured in the temperature range from 80 to 300K. Cobaltite with x ≦ 0.15 is a semiconductor, but the specimen with chemical composition 0.2 ≦ x ≦ 0.5 is metallic. The change of temperature dependence of electrical resistivity has a break point around T_c. The value of the logarithm of the specific electrical resistivity (log ?) at 300K has a minimum at x = 0.4, and this result is explained by the Zener double-exchange mechanism.     

Preparation and characterization of compounds of the system Fe(Sb1−xTex)2 (0 ⩽ x ⩽ 1.0)

The complete solid solution of Fe(Sb_1?xTe_x)₂ with the marcasite structure was synthesized. Electrical and magnetic measurements showed that the substitution of tellurium for antimony in the diamagnetic semiconductor FeSb₂ resulted in metallic and paramagnetic behavior in the composition range 0.1 ? x ? 0.3, but in 0.4 ? x ? 0.6 the products belonged to the arsenopyrite structure and were diamagnetic and semiconductive. The samples whose compositions were in the range 0.7 ? x ? 1.0 were semiconductors. Mössbauer effect measurements showed that the isomer shift did not change, but the quadrupole splitting changed significantly from 1.28 mm/sec for FeSb₂ to 0.50 mm/sec for FeTe₂ in this solid solution.     

The isotropic temperature factors of Sr(Co1−xMnx)O3 (x = 0, 0.1, 0.5, 0.8, and 1.0)

The cubic perovskite Sr(Co_1?xMn_x)O₃ has a maximum value of a-axis at x = 0.3 and a change of spin state of Co⁴⁺ ion from low to high. To elucidate these properties, the isotropic temperature factor (B) of strontium, cobalt, manganese, and oxygen atoms for x = 0, 0.1, 0.5, 0.8, and 0.1 have been derived from powder X-ray diffraction measurements. The isotropic temperature factor of oxygen for x = 0, 0.1, and 1.0 is small and that for x = 0.5 and 0.8 is large. This fact suggests that the oxygen ion deviates from the center of the CoOMn bond in the solid solutions with $\text{x ≧ 0.3}$. Larger CoO₆ octahedra and smaller MnO₆ octahedra, which are connected by corner sharing of oxygens of the octahedron, are distributed statistically.     

Synthesis of Ba(V1−xTix)S3 (0 ≦ x ≦ 1.0) compounds and their structural transitions

The two-layer hexagonal perovskites Ba(V_1?xTi_x)S₃ (0 ≦ x ≦ 1.0) are prepared in a H₂S stream. A in a H₂S stream. A structural phase transition from a hexagonal to an orthorhombic form takes place for the powder samples with 0 ≦ x ≦ 0.4 and their transition temperatures are determined to be 250 K for x = 0, 240 K for x = 0.1, 222 K for x = 0.2, 195 K for x = 0.3, and 160 K for x = 0.4, respectively. The phase transformation does not occur down to 90 K for the materials above x = 0.5.     

Hindered rotation in trimethylenemethane—Fe(CO)3 complexes

^>13C NMR spectra have been recorded for trimethylenemethane—Fe(CO)₃ (I) as well as its acetyl (II), 1-hydroxyethyl (III), 1-acetoxyethyl (IV) and ethyl (V) derivatives respectively. Compounds II–IV exhibit 3 distinct ¹³CO resonances at room temperature. These signals undergo a reversible broadening and merge into a single sharp signal on warming. δGG^? for Fe(CO)₃ rotation at the coalescence points is 17–18 kcal mol^?1. The rotational barrier is electronic in origin.     

Phases and phase transitions of compounds (CnH2n+1NH3)2MnCl4 with n = 1, 2, 3

Phases and structural phase transitions of the compounds (CH₃NH₃)₂MnCl₄, (C₂H₅NH₃)₂MnCl₄ and (C₃H₇NH₃)₂MnCl₄ have been studied by means of thermoanalytical methods (DSC) and X-ray single crystal and powder diffraction data in the temperature range of 85–480°K at normal pressure. All phases show perovskite-like layer structures. The high temperature phases (α phase) correspond to the K₂NiF₄ type and may be regarded as the aristotype of each polymorphic compound. All transitions are reversible. Transition patterns are:

Based on the DSC peak-shape analysis and diffraction data a model of a tilting system of the MnCl₆-octahedra layer is introduced in order to understand essential features of structures of different phases and their transition behavior. Single crystal film data of (C₃H₇NH₃)₂MnCl₄ phases reveal some disorder phenomena. The ε phase exhibits a superstructure along [010] with a triplication of the shortest axis corresponding to the δ phase. The γ phase of this compound shows strong satellite reflections, due to a transverse distortion wave along the [100] lattice direction.     

Three-coordinate RhX[P(C6H11)3]2, their reactions with N2 and O2, and the trans-influence in RhX[P(C6H11)3]2L (X = anionic,L = neutral ligand)

Three-coordinate RhX(PCy₃)₂ complexes (X = F, Cl, Br, I; Cy = cyclohexyl) have been prepared from rhodium(I) cyclooctene compounds. RhCl(PCy₃)₂ is in equilibrium with its dimer. The complexes RhX(PCy₃)₂ (X = Cl, Br, I) form the adducts RhX(PCy₃)₂(N₂) with dinitrogen, the times for N₂-fixation being 4 days, 3 hours and 15 minutes respectively. The three-coordinate complexes form four-coordinate dioxygen adducts RhX(PCy₃)₂(O₂) which have unusually high ν(OO) at about 990 cm^?1. This high frequency is attributed to the four-coordination, which is exceptional for dioxygen complexes. From RhF(PCy₃)₂ carbonyl, ethene, and diphenylacetylene complexes RhX(PCy₃)₂L (X = F, Cl, Br, I, N₃, NCO, NCS; L = CO, C₂H₄, C₂Ph₂) (X = CN, NO₃, acetate; L = CO) have been prepared. The trans-influence of the anionic ligands on the infrared frequencies of the neutral ligands is discussed in terms of the different π-bonding properties of the X- and L-ligands.     

The thermal dissociation of the [Co(NH3)6]Cl3 and [Co(NH3)6]Br3 complexes in vacuo

The thermal dissociation of the complexes, [Co(NH₃)₆]X₃(X^?=Cl, Br), was studied in vacuo using the techniques of thermogravimetry, evolved gas analysis and mass spectrometric analysis. It was found that the reaction stoichiometry was identical to that previously determined in air but that the type of intermediate compounds formed were different. The dissociation occurred by the reactions:

     

Preparation and properties of the systems Fe2−xCrxWO6, Fe2−xRhxWO6, and Cr2−xRhxWO6

Solid solutions of the end members Fe₂WO₆, Cr₂WO₆, and Rh₂WO₆ have been prepared and their crystallographic and magnetic properties studied. All solid solutions crystallize with the trirutile structure, and their magnetic behavior is characterized by the existence of antiferromagnetic interactions and effective molar Curie constants corresponding to those expected from contributions of the spinonly moments of high-spin Fe³⁺, Cr³⁺, and diamagnetic low-spin Rh³⁺ ions. Fe₂WO₆ crystallizes with the tri-α-PbO₂ structure and is antiferromagnetic and conducting. The random rutile Rh₂WO₆ is conducting, and the difference between its magnetic and electric properties and those of the inverse trirutile Cr₂WO₆ are discussed in terms of possible interactions between Cr³⁺(3d) or Rh³⁺(4d) orbitals and W⁶⁺(5d) orbitals.     

Massenspektrometrische-, dta- und tg-untersuchungen an eisencarbonylchalkogeniden Fe2(CO)6X2 (X  S,Se) und Fe3(CO)9X′2 (X′  S,Se, Te)

Mass spectra of Fe₃(CO)₉X₂ (X  S, Se, Te) and Fe₂(CO)₆X′₂ (X′  S, Se) are recorded and their fragmentation pattern given. The thermal decarbonylation has been studied using DTA/TG methods in the temperature range 25–600°C. The results are compared with those obtained from mass-spectroscopic studies. X-ray and magnetic measurements have been carried out on the residues obtained in the decarbonylation process.     

Polarized crystal spectra of the mixed metal salt [(CH3)3NH]MnxCu1−xCl3·2H2O

The electronic absorption spectra in two polarizations are reported for crystals of the dichroic salt, TMAMn_xCu_1?xCl₃·2H₂O where TMA represents the trimethylammonium cation, (CH₃)₃NH⁺. Although TMACuCl₃·2H₂O is monoclinic, the mixed metal salts in which x ≥ 0.20 adopt the orthorhombic structure of TMAMnCl₃·2H₂O. The bands observed in the near ir region are adequately explained as d-d transitions of the Cu(II) ion in D_2h symmetry. Other polarized bands which occur in the visible region and are neither Mn(II) nor Cu(II) d-d transitions are discussed.     

Darstellung und chemie von Me2TlN(SiMe3)2 und Tl[N(SiMe3)2]3

The complexes [Rh(η³-C₃H₄R)(η⁵-C₅R′₅)L]⁺BF₄^- (R  1-Me, R′  H, Me; R  2-Me, R′  H) (L  C₅H₅N, Ph₃P, Ph₃As) have been prepared from Rh(η³-C₃H₄R)(η⁵-C₅R′₅)Cl and AGBF₄ in acetone, followed by reaction with the stoicheiometric quantity of L. The ¹H and ¹³C NMR spectra of the salts are reported and discussed.     

The electrical,optical and photoconducting properties of Fe2−xCrxO3 (0 ⩽ x ⩽ 0.47)

A study has been made of the electrical, optical and photoconducting properties of pure and reduced single crystals of composition Fe_2?xCr_xO₃ where 0 ? x ? 0.47. It has been found that pure α-Fe₂O₃ is not a photoconductor. When defect-free crystals of α-Fe₂O₃ are reduced a surface layer of Fe₃O₄ is formed and the crystals exhibit photoconductivity. Removal of this layer resulted in the disappearance of photocurrents and an increase in the sample resistivity. A necessary condition for the observation of photocurrents in n-type Fe₂O₃ is that some Fe₃O₄ be present. In addition, it has been found that the substitution of chromium for iron in α-Fe₂O₃ results in a monotonically decreasing optical band gap as the chromium concentration, x, increases.     

The thermal dissociation of the [Co(en)3](SCN)3 and [Co(en)3]I3 complexes

The thermal dissociation of the [Co(en)₃](SCN)₃ and [Co(en)₃]I₃ complexes was studied by thermogravimetry, differential thermal analysis, thermomagnetic analysis, pyrolytic techniques, evolved gas analysis, and mass spectrometry, in vacuo and nitrogen atmospheres. It was found that the [Co(en)₃](SCN)₃ complex dissociated in four steps:

It was not possible to elucidate the intermediate compounds formed in the thermal dissociation of the [Co(en)₃]I₃ complex.     

Magnetic resonance study of (GdxY1−x)Co2 compounds

The results of magnetic resonance studies on ferrimagnetic (Gd_xY_1?x)Co₂ compounds, both below and above the Curie points, are presented. The ferrimagnetic resonance measurements show that the effective g values can be described by using the Wangsness relation. The spectroscopic splitting factors of cobalt atoms are not composition dependent. In the paramagnetic range the thermal variation of the linewidth is not linear and the g values are a function of temperature. This behavior is analyzed in correlation with the magnetic data.     

Synthesis and reactions of the transition metal substituted tin hydride HSn[Mo(CO)3C5H5]3

Reaction of HMo(CO)₃C₅H₅ and Sn(C₅H₅)₂ produces the tin hydride HSn[Mo(CO)₃C₅H₅]₃ (I). Reaction of I with CCl₄, CHCl₃, or CH₂Cl₂ gives ClSn[Mo(CO)₃C₅H₅]₃ (II). With hydrogen chloride the hydride I reacts to produce the dichloride Cl₂Sn[Mo(CO)₃C₅H₅]₂. The first step in this reaction is cleavage of the SnH bond to produce the chloride II. The hydride I reacts with acetic acid to produce the diacetate (CH₃COO)₂Sn[Mo(CO)₃C₅H₅]₂.     

Phase transitions in a Cs2−xK1+xBiCl6 solid solution

A solid solution with a Cs_2?xK_1+xBiCl₆ (0 ≤ x ≤ 1) formulation and an elpasolite-related structure was prepared. At room temperature the symmetry is cubic (Fm3m) for x = 0 and triclinic $\text{(P}\text{I}\text{)}$ for x ≠ 0. For 0 ≤ x ≤ 1, various techniques enabled us to detect a phase transition of the ferroelastic-paraelastic type at t_c (°C) temperature. The t_c and ΔH_tc values are correlated to the size of the alkali ions.